Biorefineries producing commodities from renewable resources offer an alternative to oil refineries based on dwindling supplies of petroleum and permit a move towards improved energy security. Lignocellulosic materials from forestry and agriculture are attractive as feedstocks, since they are abundant, relatively inexpensive, and are not used for food. Lignocellulose consists mainly of lignin and two classes of polysaccharides, cellulose and hemicellulose. The polysaccharides can be hydrolyzed to sugars and converted to various fermentation products, such as bioalcohols, in processes based on biocatalysts, such as the industrially important baker's yeast (Saccharomyces cerevisiae).
The hydrolysis of cellulose may be preceded by a pretreatment, in which the hemicellulose is degraded and the cellulose is made increasingly accessible to cellulolytic enzymes or acidic hydrolysis, see e.g. Alvira et al and Harmsen et al.
By using enzymatic hydrolysis, hydrolysis and fermentation can be performed simultaneously in a simultaneous saccharification and fermentation (SSF) process or in a consolidated bioprocess (CBP). Alternatively, separate hydrolysis and fermentation (SHF) can be used, a process configuration that may also include enzyme-based hydrolysis of the cellulose.